/*
 * Copyright (c) 2013, SRI International
 * All rights reserved.
 * Licensed under the The BSD 3-Clause License;
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 * 
 * http://opensource.org/licenses/BSD-3-Clause
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 * Redistributions of source code must retain the above copyright
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 * Neither the name of the aic-expresso nor the names of its
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package com.sri.ai.grinder.library.controlflow;

import com.google.common.annotations.Beta;
import com.sri.ai.expresso.api.Expression;
import com.sri.ai.grinder.api.RewritingProcess;
import com.sri.ai.grinder.core.AbstractRewriter;
import com.sri.ai.grinder.core.HasKind;
import com.sri.ai.grinder.library.Disequality;
import com.sri.ai.grinder.library.Equality;
import com.sri.ai.grinder.library.FunctorConstants;

/**
 * An atomic rewriter for rewriting expressions of the type 'if X != c then Alpha else Beta' to 'if X = c then Beta else Alpha'.
 * This is easier to read and allows for further simplifications.
 * 
 * @author braz
 *
 */
@Beta
public class DisequalityToEqualityInIfThenElseCondition extends AbstractRewriter {
	
	public DisequalityToEqualityInIfThenElseCondition() {
		this.setReifiedTests(new HasKind(FunctorConstants.IF_THEN_ELSE));
	}

	@Override
	public Expression rewriteAfterBookkeeping(Expression expression, RewritingProcess process) {
		Expression condition;
		if (IfThenElse.isIfThenElse(expression) &&
				Disequality.isDisequality(condition = IfThenElse.getCondition(expression))) {
			
			Expression equality = Equality.make(condition.getArguments());
			equality = Equality.normalize(equality, process);
			Expression thenBranch = IfThenElse.getThenBranch(expression);
			Expression elseBranch = IfThenElse.getElseBranch(expression);
			Expression result = IfThenElse.make(equality, elseBranch, thenBranch);
			return result;
		}
		return expression;
	}
}
